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 * Copyright (c) 1995, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.io;

/**
 * A piped input stream should be connected
 * to a piped output stream; the piped  input
 * stream then provides whatever data bytes
 * are written to the piped output  stream.
 * Typically, data is read from a <code>PipedInputStream</code>
 * object by one thread  and data is written
 * to the corresponding <code>PipedOutputStream</code>
 * by some  other thread. Attempting to use
 * both objects from a single thread is not
 * recommended, as it may deadlock the thread.
 * The piped input stream contains a buffer,
 * decoupling read operations from write operations,
 * within limits.
 * A pipe is said to be <a name="BROKEN"> <i>broken</i> </a> if a
 * thread that was providing data bytes to the connected
 * piped output stream is no longer alive.
 *
 * @author James Gosling
 * @see java.io.PipedOutputStream
 * @since JDK1.0
 */
public class PipedInputStream extends InputStream {

  boolean closedByWriter = false;
  volatile boolean closedByReader = false;
  boolean connected = false;

  /* REMIND: identification of the read and write sides needs to be
     more sophisticated.  Either using thread groups (but what about
     pipes within a thread?) or using finalization (but it may be a
     long time until the next GC). */
  Thread readSide;
  Thread writeSide;

  private static final int DEFAULT_PIPE_SIZE = 1024;

  /**
   * The default size of the pipe's circular input buffer.
   *
   * @since JDK1.1
   */
  // This used to be a constant before the pipe size was allowed
  // to change. This field will continue to be maintained
  // for backward compatibility.
  protected static final int PIPE_SIZE = DEFAULT_PIPE_SIZE;

  /**
   * The circular buffer into which incoming data is placed.
   *
   * @since JDK1.1
   */
  protected byte buffer[];

  /**
   * The index of the position in the circular buffer at which the
   * next byte of data will be stored when received from the connected
   * piped output stream. <code>in&lt;0</code> implies the buffer is empty,
   * <code>in==out</code> implies the buffer is full
   *
   * @since JDK1.1
   */
  protected int in = -1;

  /**
   * The index of the position in the circular buffer at which the next
   * byte of data will be read by this piped input stream.
   *
   * @since JDK1.1
   */
  protected int out = 0;

  /**
   * Creates a <code>PipedInputStream</code> so
   * that it is connected to the piped output
   * stream <code>src</code>. Data bytes written
   * to <code>src</code> will then be  available
   * as input from this stream.
   *
   * @param src the stream to connect to.
   * @throws IOException if an I/O error occurs.
   */
  public PipedInputStream(PipedOutputStream src) throws IOException {
    this(src, DEFAULT_PIPE_SIZE);
  }

  /**
   * Creates a <code>PipedInputStream</code> so that it is
   * connected to the piped output stream
   * <code>src</code> and uses the specified pipe size for
   * the pipe's buffer.
   * Data bytes written to <code>src</code> will then
   * be available as input from this stream.
   *
   * @param src the stream to connect to.
   * @param pipeSize the size of the pipe's buffer.
   * @throws IOException if an I/O error occurs.
   * @throws IllegalArgumentException if {@code pipeSize <= 0}.
   * @since 1.6
   */
  public PipedInputStream(PipedOutputStream src, int pipeSize)
      throws IOException {
    initPipe(pipeSize);
    connect(src);
  }

  /**
   * Creates a <code>PipedInputStream</code> so
   * that it is not yet {@linkplain #connect(java.io.PipedOutputStream)
   * connected}.
   * It must be {@linkplain java.io.PipedOutputStream#connect(
   *java.io.PipedInputStream) connected} to a
   * <code>PipedOutputStream</code> before being used.
   */
  public PipedInputStream() {
    initPipe(DEFAULT_PIPE_SIZE);
  }

  /**
   * Creates a <code>PipedInputStream</code> so that it is not yet
   * {@linkplain #connect(java.io.PipedOutputStream) connected} and
   * uses the specified pipe size for the pipe's buffer.
   * It must be {@linkplain java.io.PipedOutputStream#connect(
   *java.io.PipedInputStream)
   * connected} to a <code>PipedOutputStream</code> before being used.
   *
   * @param pipeSize the size of the pipe's buffer.
   * @throws IllegalArgumentException if {@code pipeSize <= 0}.
   * @since 1.6
   */
  public PipedInputStream(int pipeSize) {
    initPipe(pipeSize);
  }

  private void initPipe(int pipeSize) {
    if (pipeSize <= 0) {
      throw new IllegalArgumentException("Pipe Size <= 0");
    }
    buffer = new byte[pipeSize];
  }

  /**
   * Causes this piped input stream to be connected
   * to the piped  output stream <code>src</code>.
   * If this object is already connected to some
   * other piped output  stream, an <code>IOException</code>
   * is thrown.
   * <p>
   * If <code>src</code> is an
   * unconnected piped output stream and <code>snk</code>
   * is an unconnected piped input stream, they
   * may be connected by either the call:
   *
   * <pre><code>snk.connect(src)</code> </pre>
   * <p>
   * or the call:
   *
   * <pre><code>src.connect(snk)</code> </pre>
   * <p>
   * The two calls have the same effect.
   *
   * @param src The piped output stream to connect to.
   * @throws IOException if an I/O error occurs.
   */
  public void connect(PipedOutputStream src) throws IOException {
    src.connect(this);
  }

  /**
   * Receives a byte of data.  This method will block if no input is
   * available.
   *
   * @param b the byte being received
   * @throws IOException If the pipe is <a href="#BROKEN"> <code>broken</code></a>, {@link
   * #connect(java.io.PipedOutputStream) unconnected}, closed, or if an I/O error occurs.
   * @since JDK1.1
   */
  protected synchronized void receive(int b) throws IOException {
    checkStateForReceive();
    writeSide = Thread.currentThread();
    if (in == out) {
      awaitSpace();
    }
    if (in < 0) {
      in = 0;
      out = 0;
    }
    buffer[in++] = (byte) (b & 0xFF);
    if (in >= buffer.length) {
      in = 0;
    }
  }

  /**
   * Receives data into an array of bytes.  This method will
   * block until some input is available.
   *
   * @param b the buffer into which the data is received
   * @param off the start offset of the data
   * @param len the maximum number of bytes received
   * @throws IOException If the pipe is <a href="#BROKEN"> broken</a>, {@link
   * #connect(java.io.PipedOutputStream) unconnected}, closed,or if an I/O error occurs.
   */
  synchronized void receive(byte b[], int off, int len) throws IOException {
    checkStateForReceive();
    writeSide = Thread.currentThread();
    int bytesToTransfer = len;
    while (bytesToTransfer > 0) {
      if (in == out) {
        awaitSpace();
      }
      int nextTransferAmount = 0;
      if (out < in) {
        nextTransferAmount = buffer.length - in;
      } else if (in < out) {
        if (in == -1) {
          in = out = 0;
          nextTransferAmount = buffer.length - in;
        } else {
          nextTransferAmount = out - in;
        }
      }
      if (nextTransferAmount > bytesToTransfer) {
        nextTransferAmount = bytesToTransfer;
      }
      assert (nextTransferAmount > 0);
      System.arraycopy(b, off, buffer, in, nextTransferAmount);
      bytesToTransfer -= nextTransferAmount;
      off += nextTransferAmount;
      in += nextTransferAmount;
      if (in >= buffer.length) {
        in = 0;
      }
    }
  }

  private void checkStateForReceive() throws IOException {
    if (!connected) {
      throw new IOException("Pipe not connected");
    } else if (closedByWriter || closedByReader) {
      throw new IOException("Pipe closed");
    } else if (readSide != null && !readSide.isAlive()) {
      throw new IOException("Read end dead");
    }
  }

  private void awaitSpace() throws IOException {
    while (in == out) {
      checkStateForReceive();

            /* full: kick any waiting readers */
      notifyAll();
      try {
        wait(1000);
      } catch (InterruptedException ex) {
        throw new java.io.InterruptedIOException();
      }
    }
  }

  /**
   * Notifies all waiting threads that the last byte of data has been
   * received.
   */
  synchronized void receivedLast() {
    closedByWriter = true;
    notifyAll();
  }

  /**
   * Reads the next byte of data from this piped input stream. The
   * value byte is returned as an <code>int</code> in the range
   * <code>0</code> to <code>255</code>.
   * This method blocks until input data is available, the end of the
   * stream is detected, or an exception is thrown.
   *
   * @return the next byte of data, or <code>-1</code> if the end of the stream is reached.
   * @throws IOException if the pipe is {@link #connect(java.io.PipedOutputStream) unconnected}, <a
   * href="#BROKEN"> <code>broken</code></a>, closed, or if an I/O error occurs.
   */
  public synchronized int read() throws IOException {
    if (!connected) {
      throw new IOException("Pipe not connected");
    } else if (closedByReader) {
      throw new IOException("Pipe closed");
    } else if (writeSide != null && !writeSide.isAlive()
        && !closedByWriter && (in < 0)) {
      throw new IOException("Write end dead");
    }

    readSide = Thread.currentThread();
    int trials = 2;
    while (in < 0) {
      if (closedByWriter) {
                /* closed by writer, return EOF */
        return -1;
      }
      if ((writeSide != null) && (!writeSide.isAlive()) && (--trials < 0)) {
        throw new IOException("Pipe broken");
      }
            /* might be a writer waiting */
      notifyAll();
      try {
        wait(1000);
      } catch (InterruptedException ex) {
        throw new java.io.InterruptedIOException();
      }
    }
    int ret = buffer[out++] & 0xFF;
    if (out >= buffer.length) {
      out = 0;
    }
    if (in == out) {
            /* now empty */
      in = -1;
    }

    return ret;
  }

  /**
   * Reads up to <code>len</code> bytes of data from this piped input
   * stream into an array of bytes. Less than <code>len</code> bytes
   * will be read if the end of the data stream is reached or if
   * <code>len</code> exceeds the pipe's buffer size.
   * If <code>len </code> is zero, then no bytes are read and 0 is returned;
   * otherwise, the method blocks until at least 1 byte of input is
   * available, end of the stream has been detected, or an exception is
   * thrown.
   *
   * @param b the buffer into which the data is read.
   * @param off the start offset in the destination array <code>b</code>
   * @param len the maximum number of bytes read.
   * @return the total number of bytes read into the buffer, or <code>-1</code> if there is no more
   * data because the end of the stream has been reached.
   * @throws NullPointerException If <code>b</code> is <code>null</code>.
   * @throws IndexOutOfBoundsException If <code>off</code> is negative, <code>len</code> is
   * negative, or <code>len</code> is greater than <code>b.length - off</code>
   * @throws IOException if the pipe is <a href="#BROKEN"> <code>broken</code></a>, {@link
   * #connect(java.io.PipedOutputStream) unconnected}, closed, or if an I/O error occurs.
   */
  public synchronized int read(byte b[], int off, int len) throws IOException {
    if (b == null) {
      throw new NullPointerException();
    } else if (off < 0 || len < 0 || len > b.length - off) {
      throw new IndexOutOfBoundsException();
    } else if (len == 0) {
      return 0;
    }

        /* possibly wait on the first character */
    int c = read();
    if (c < 0) {
      return -1;
    }
    b[off] = (byte) c;
    int rlen = 1;
    while ((in >= 0) && (len > 1)) {

      int available;

      if (in > out) {
        available = Math.min((buffer.length - out), (in - out));
      } else {
        available = buffer.length - out;
      }

      // A byte is read beforehand outside the loop
      if (available > (len - 1)) {
        available = len - 1;
      }
      System.arraycopy(buffer, out, b, off + rlen, available);
      out += available;
      rlen += available;
      len -= available;

      if (out >= buffer.length) {
        out = 0;
      }
      if (in == out) {
                /* now empty */
        in = -1;
      }
    }
    return rlen;
  }

  /**
   * Returns the number of bytes that can be read from this input
   * stream without blocking.
   *
   * @return the number of bytes that can be read from this input stream without blocking, or {@code
   * 0} if this input stream has been closed by invoking its {@link #close()} method, or if the pipe
   * is {@link #connect(java.io.PipedOutputStream) unconnected}, or <a href="#BROKEN">
   * <code>broken</code></a>.
   * @throws IOException if an I/O error occurs.
   * @since JDK1.0.2
   */
  public synchronized int available() throws IOException {
    if (in < 0) {
      return 0;
    } else if (in == out) {
      return buffer.length;
    } else if (in > out) {
      return in - out;
    } else {
      return in + buffer.length - out;
    }
  }

  /**
   * Closes this piped input stream and releases any system resources
   * associated with the stream.
   *
   * @throws IOException if an I/O error occurs.
   */
  public void close() throws IOException {
    closedByReader = true;
    synchronized (this) {
      in = -1;
    }
  }
}
